Heat Exchanger Using Non-Pure Water for Steam Generation

ABSTRACT

A process and a device are described for producing high purity and high temperature steam from non-pure water which may be used in a variety of industrial processes that involve high temperature heat applications. The process and device may be used with technologies that generate steam using a variety of heat sources, such as, for example industrial furnaces, petrochemical plants, and emissions from incinerators. Of particular interest is the application in a thermochemical hydrogen production cycle such as the Cu—Cl Cycle. Non-pure water is used as the feedstock in the thermochemical hydrogen production cycle, with no need to adopt additional and conventional water pre-treatment and purification processes. The non-pure water may be selected from brackish water, saline water, seawater, used water, effluent treated water, tailings water, and other forms of water that is generally believed to be unusable as a direct feedstock of industrial processes. The direct usage of this water can significantly reduce water supply costs.

TECHNICAL FIELD

A process and a device are described for producing high purity and hightemperature steam from non-pure water which may be used in a variety ofindustrial processes that involve high temperature heat applications.The process and device may be used with technologies that generate steamusing a variety of heat sources, such as, for example industrialfurnaces, petrochemical plants, and emissions from incinerators. Ofparticular interest is the application in a thermochemical hydrogenproduction cycle. Non-pure water is used as the feedstock in thethermochemical hydrogen production cycle, with no need to adoptadditional and conventional water pre-treatment and purificationprocesses. The non-pure water may be selected from lake water, brackishwater, saline water, seawater, used water, effluent treated water,tailings water, and other forms of water that are generally believed tobe unusable as a direct feedstock of industrial processes. The directusage of this water significantly reduces water supply costs.

BACKGROUND

Hydrogen is widely believed to be one of the world's next generationfuels, since its oxidation does not emit greenhouse gases thatcontribute to climate change. Auto manufacturers are investingsignificantly in hydrogen vehicles. Other transportation vehicles, suchas ships, trains and utility vehicles also represent promisingopportunities for use of hydrogen fuel. Hydrogen is also a majornecessity for the upgrading of heavy oils and fertilizer production.Thus there is need for a reliable, safe, efficient and economic processfor the production of hydrogen gas for fuel, heavy oil upgrading andfertilizer production.

Electrolysis is a proven, commercial technology that separates waterinto hydrogen and oxygen using electricity. Net electrolysisefficiencies are typically about 24%. In contrast, thermochemicalreactions to produce hydrogen using nuclear heat can achieveheat-to-hydrogen efficiencies up to about 50% [See Schultz, K., Herring,S., Lewis M., Summers, W., “The Hydrogen Reaction”, Nuclear EngineeringInternational, vol. 50, pp. 10-19, 2005 and Rosen, M. A., “ThermodynamicComparison of Hydrogen Production Processes”, International Journal ofHydrogen Energy, vol. 21, no. 5, pp. 349-365, 1996.]

A copper-chlorine (Cu—Cl) cycle has been identified by Atomic Energy ofCanada Ltd. (AECL) [See Sadhankar, R. R., Li, J, Li, H., Ryland, D. K.,Suppiah, S. “Future Hydrogen Production Using Nuclear Reactors”,Engineering Institute of Canada—Climate Change Technology Conference,Ottawa, May, 2006 and Sadhankar, R. R., “Leveraging Nuclear Research toSupport Hydrogen Economy”, 2nd Green Energy Conference, Oshawa, June,2006.] at its Chalk River Laboratories (CRL) as a highly promisingthermochemical cycle for hydrogen production. Water is decomposed intohydrogen and oxygen through intermediate Cu and Cl compounds. Paststudies at Argonne National Laboratory (ANL) have developed enablingtechnologies for the Cu—Cl thermochemical cycle, through anInternational Nuclear Energy Research Initiative (INERI), as reported byLewis et al. [See 17. Lewis, M. A., Serban, M., Basco, J. K, “HydrogenProduction at <550° C. Using a Low Temperature Thermochemical Cycle”,ANS/ENS Exposition, New Orleans, November, 2003.] The Cu—Cl cycle iswell matched to Canada's nuclear reactors, since its heat requirementfor high temperatures is adaptable to the Super-Critical Water Reactor(SCWR), which is being considered as Canada's Generation IV nuclearreactor.

Other countries (Japan, U.S. and France) are currently advancing nucleartechnology for thermochemical hydrogen production [See Sakurai, M.,Nakajima, H., Amir, R., Onuki, K., Shimizu, S., “Experimental Study onSide-Reaction Occurrence Condition in the Iodine-Sulfur ThermochemicalHydrogen Production Process”, International Journal of Hydrogen Energy,vol. 23, pp. 613-619, 2000; Schultz, K., “Thermochemical Production ofHydrogen from Solar and Nuclear Energy”, Technical Report for theStanford Global Climate and Energy Project, General Atomics, San Diego,Calif., 2003; and Doctor, R. D., Matonis, D. T., Wade, D. C, “HydrogenGeneration Using a Calcium - Bromine Thermochemical Water-splittingCycle”, Paper ANL/ES/CP-3-111623, OECD 2nd Information Exchange Meetingon Nuclear Production of Hydrogen, Argonne, Ill., Oct. 2-3, 2003.]

The Sandia National Laboratory in the U.S. and CEA in France aredeveloping a hydrogen pilot plant with a sulphur-iodine (S—I) cycle [SeePickard, P., Gelbard, F., Andazola, J., Naranjo, G., Besenbruch, G.,Russ, B., Brown, L., Buckingham, R., Henderson, D., “Sulfur-IodineThermochemical Cycle”, DOE Hydrogen Production Report, U.S. Departmentof Energy, Washington, D.C., 2005 Fuel Cell Vehicles: Race to a NewAutomotive Future, Office of Technology Policy, US Department ofCommerce, January, 2003.] The Korean KAERI Institute is collaboratingwith Japan Atomic Energy Agency (JAEA) aims to complete a large S—Iplant to produce 60,000 m³/hr of hydrogen by 2020, which will besufficient for about 1 million fuel cell vehicles [See Suppiah, S., Li,J., Sadhankar, R., Kutchcoskie, K. J., Lewis, M., “Study of Hybrid CuClCycle for Nuclear Hydrogen Production”, Third Information ExchangeMeeting on the Nuclear Production of Hydrogen, Orai, Japan, October,2005.] Several countries, participating in the Generation IVInternational Forum plan to develop the technologies for co-generationof hydrogen by high-temperature thermochemical cycles and electrolysis,through multilateral collaborations [See Rosen, M. A., “ThermodynamicAnalysis of Hydrogen Production by Thermochemical Water Decompositionusing the Ispra Mark-10 Cycle”, In Hydrogen Energy Prog. VIII: Proc. 8thWorld Hydrogen EnergyConference, ed. T. N. Veziroglu and P. K.Takahashi, Pergamon, Toronto, pp. 701-710, 1990.]

When compared to other methods of hydrogen production, thethermochemical Cu—Cl cycle has its own unique advantages, challenges,risks and limitations. Technical challenges include the transport ofsolids and electrochemical processes of copper electrowinning, which arenot needed by other cycles such as the sulfur-iodine cycle. Theseprocesses are challenging due to solids injection/removal, which canblock equipment operation and generate undesirable side reactions indownstream chemical reactors. Flow of solid materials can lead toincreased maintenance costs, due to wear and increased downtime arisingfrom blockage and unscheduled equipment failure. A technological riskinvolves the potential use of expensive new materials of constructionthat are needed to prevent corrosion of equipment surfaces. Theseinclude surfaces exposed to molten CuCl, spray drying of aqueous CuCl₂and high temperature HCl and O₂ gases. Additional operational challengesentail the steps of chemical separation (which increases complexity andcosts) and phase separation (particles, gas, and liquids must beseparated from each other in fluid streams leaving the reactors). As aresult, the overall cycle efficiency becomes a limitation, wherein theCu—Cl cycle must compete economically against other existingtechnologies of hydrogen production.

Despite these challenges and risks, the Cu—Cl cycle offers a number ofkey advantages over other cycles of thermochemical hydrogen production.The attractions include lower temperatures compared to other cycles likethe S—I cycle. Heat input at temperatures less than 530° C. make itsuitable for coupling to Canada's SCWR (Super-Critical Water Reactor;Generation IV nuclear reactor) and reduced demands on materials ofconstruction. Other advantages are inexpensive raw materials andreactions that proceed nearly to completion without significant sidereactions. Solids handling is required, but it is relatively minimal andit can be reduced by combining thermochemical and electrochemical stepstogether. Another key advantage is the cycle's ability to utilizelow-grade waste heat from power plants, for various thermal processeswithin the cycle. US Patent Publication No. 2010/012987, published May27, 2010 describes a system utilizing a thermochemical CuCl cycle indetail. The disclosures of this application are incorporated herein intheir entirety.

There is a need to improve the efficiency of the Cu—Cl cycle for it tobe competitive and all aspects of the cycle need to be examined for suchopportunities.

SUMMARY

This disclosure related to an improved high temperature industrialprocess where heat recovery is desired, the improvement comprisingtransferring heat from a high temperature molten or gaseous materialobtained in the high temperature industrial process, to generate hightemperature steam from non-pure water, with the impurities in the waterbeing reduced to a precipitate, a slurry or a concentrated aqueoussolution, which can be disposed of, or subjected to further processing.

More specifically, high temperature steam is generated in a heatexchange process, wherein heat from high temperature molten or gaseousmaterial is supplied to non-pure water to produce high temperaturesteam, with the impurities in the water being reduced to a precipitate,a slurry or a concentrated aqueous solution, which can be disposed of,or subjected to further processing.

In another form of the process, where high temperature steam isgenerated in a heat exchange process, the steam is generated from atwo-stage steam generation loop which comprises two heat exchanges, afirst-stage heat exchange comprising transferring heat from moltenmaterial to a thermal fluid circulating to a second-stage heat exchange,and back again to the first-stage heat exchange; heat from the thermalfluid being transferred to non-pure water in the second-stage heatexchange to produce high temperature steam from which hydrogen gas isproduced, and impurities in the water are reduced to a precipitate, aslurry or a concentrated aqueous solution, which can be disposed of, orsubjected to further processing.

In a particular form, the industrial process is a thermochemical Cu—Clcycle for producing hydrogen gas from water decomposition whichcomprises supplying heat to the non-pure water from molten CuCl toproduce high temperature steam for the production of hydrogen gas, withthe impurities in the water being reduced to a precipitate, a slurry ora concentrated aqueous solution, which can be disposed of, or subjectedto further processing.

When the industrial process is a thermochemical Cu—Cl cycle forproducing hydrogen gas from water decomposition, it may comprise thegeneration of steam from non-pure water using a two-stage steamgeneration loop which comprises two heat exchanges, a first-stage heatexchange comprising transferring heat from molten CuCl to a thermalfluid circulating to a second-stage heat exchange, and back again to thefirst-stage heat exchange; heat from the thermal fluid being transferredto non-pure water in the second-stage heat exchange to produce hightemperature steam from which hydrogen gas is produced, and impurities inthe water are reduced to a precipitate, a slurry or a concentratedaqueous solution, which can be disposed of, or subjected to furtherprocessing.

There is also disclosed a device for use in a high temperatureindustrial process where heat recovery is required and high temperaturesteam is produced which comprises using a tube and shell heat exchanger,the tube is arranged to receive a high temperature molten or gaseousmaterial obtained from the high temperature industrial process and theshell is arranged to receive non-pure water to which heat is transferredfrom the high temperature molten or gaseous material in the tube, whichthen generates high temperature steam from the non-pure water, with theimpurities in the non-pure water being reduced to a precipitate, aslurry or a concentrated aqueous solution, which can be disposed of, orsubjected to further processing.

In another form, the device is for use in a high temperature industrialprocess where heat recovery is desired and high temperature steam isproduced, and comprises a two-stage steam generation loop whichcomprises two heat exchangers, each having a central tube andsurrounding shell, the first-stage heat exchanger arranged for hightemperature molten or gaseous material to pass through its central tubeand the surrounding shell is arranged to receive a secondary thermalfluid to circulate in the surrounding shell to absorb heat from the hightemperature molten or gaseous material, the surrounding shell being influid communication with the shell in the second-stage heat exchanger topermit circulation of the heated thermal fluid from one shell to theother and back again to the shell in the first-stage heat exchanger; thecentral tube of the second stage heat exchanger arranged to receivenon-pure water which absorbs heat from the thermal fluid to generatehigh temperature steam for use in the high temperature industrialprocess, and impurities in the water are reduced to a precipitate, aslurry or a concentrated aqueous solution which can be disposed of orsubjected to further processing.

When the industrial process is a thermochemical Cu—Cl cycle for theproduction of hydrogen from water decomposition and the molten materialis CuCl salt, the high temperature steam is used to produce hydrogen gasfrom decomposition of water in the thermochemical CuCl cycle.

The molten CuCl may be received in the tube of the heat exchanger andpasses therethrough with the assistance of at least one of gravity, apush-pull plate or a helical screw.

The molten CuCl may pass through the tube of the heat exchanger at arate that allows the production of high temperature steam at atemperature suitable for the production of hydrogen gas from thedecomposition of water in the thermochemical CuCl cycle. The tube wallmay be treated with lubricant to assist passage of molten CuCl throughthe tube of the heat exchanger, in at least one of the following ways:in advance of the device being used, on a periodic basis and on acontinuous basis during use of the device.

The shell walls may be washed with water or water containing cleaners orboth to remove any adhered impurities that foul the apparatus, thewashing taking place either when the device is in use or when the deviceis not in use.

Finally, a helical screw is best used as it not only assists the passageof molten CuCl through the tube, but also facilitates passage as thesalt passes from a molten state to a solid state, as well as making theheat transfer from the molten CuCl to the non-pure water most efficient.

A unique characteristic of the process and device disclosed herein isthat non-pure water is the feedstock used to produce high purity, hightemperature steam. Normally in the Cu—Cl cycle, the water used ispurified prior to use, a step which is costly and usually eliminates thepossibility of using water that contains impurities or salts.Thermochemical hydrogen production is a desirable technology forsupplying hydrogen and oxygen at lower cost and reducing environmentalimpact as compared with existing technologies, for applications torefining, upgrading, and other petrochemical plant operations. Water,heat and a minor amount of electricity are used as inputs to producehydrogen and oxygen, without any internal consumption of materials, orexternal emissions to the environment. It has now been found that theCu—Cl cycle is capable of utilizing non-pure water as feedstock andvarious grades of waste heat from nuclear, solar, geothermal, andpetrochemical operations, such as, for example from upgraders,gasifiers, and engines for equipment may be used to heat the non-purewater to produce high temperature steam of high purity with anyimpurities and salts present in the water being removed as precipitates,or slurry or both, any valuable material being recovered.

The non-pure water may be lake water, brackish water, saline water,seawater, tailings water, effluent treated water, and used water fromdrilling wells. The heat exchanger steam generator may include a screwextruder, or a pull and push plate extruder, or a casting extruder,which allows recovery of heat from molten CuCl, high temperature O₂,high temperature H₂, high temperature HCl, or other high temperaturesubstances and exothermic processes of the Cu—Cl cycle to a surroundingwater jacket. In the present application, the use of the heatexchanger-steam generator is described with respect to the Cu—Cl cycleand the heat is obtained from molten CuCl salt. A person skilled in theart can readily adapt the equipment and process to accommodate differentheat sources. The steam generation may alternatively comprise atwo-stage heat exchanger which uses a secondary thermal fluid other thanwater. In the first stage, the secondary thermal fluid flows through thesaid jacket to extract the heat from molten salt, and then in the secondstage, steam is generated from the secondary fluid using another heatexchanger.

Any indirect contact between molten salt (or high temperature gas as itoccurs in the S—I cycle) and non-fresh water can generate steam, so thesteam generation is not limited to a thermochemical cycle of hydrogenproduction, but may be utilized in other high temperature heat recoveryapplications such as industrial furnaces, petrochemical plantsemissions, and incinerators. For the example of the Cu—Cl cycle, theonly feedstock is non-pure water and the products are hydrogen andoxygen, with no other waste streams flowing, except salts and otherimpurities for the case of brackish water. The main energy input to theCu—Cl cycle is heat, significantly recycled internally or low-gradeheat. In the Cu—Cl cycle, steam reacts with auxiliary compounds of Cuand Cl to form intermediates, then hydrogen and oxygen are released fromthe intermediates, while the intermediates are recycled internallywithout being consumed.

The non-pure water is directly fed into the Cu—Cl hydrogen productioncycle without using additional heat in the present apparatus andprocesses. In comparison, other hydrogen production cycles must utilizewater that is treated and purified in a separate process, and additionalenergy must be input for the treatment and purification. The typicaldistribution of energy requirements of the Cu—Cl cycle are shown in theaccompanying drawings.

When non-pure water is used as the direct feedstock of the Cu—Cl cycle,the non-pure water is used directly without further external thermalenergy input for the processing. Other processes of the Cu—Cl cyclestill need further external thermal energy input for the thermochemicalhydrogen production.

Previously, if non-pure water was used, it was preferably used afteradditional treatment and purification, but the treatment andpurification requirements set out herein are simpler than for othertraditional steam generators.

Non-pure water, before it can be used, preferably requires additionalwater treatment and/or purification which involves additional energybefore it can be used in a Cu—Cl thermochemical hydrogen production. Thetreatment and purification requirements of the present disclosure aresimpler and the additional energy required thereof is much less than forother traditional steam generators.

Cu—Cl cycles are known in the art and may comprise a number of variants.For example, the Cu—Cl cycle may comprise a five step process comprisingthe steps of

-   -   1) reacting Cu and dry HCl gas at a temperature of about 450° C.        to obtain hydrogen gas and molten CuCl salt;    -   2) subjecting solid CuCl and HCl to electrolysis at a        temperature of about 70 to about 90° C. to obtain Cu and an        aqueous slurry containing HCl and CuCl₂;    -   3) heating the aqueous slurry obtained from step 2 at a        temperature of from about 375 to about 450° C. to obtain solid        CuCl₂ and H₂O/HCl vapours;    -   4) heating the solid CuCl₂ and water/steam to obtain solid        CuOCuCl₂ and gaseous HCl; and    -   5) heating the solid CuOCuCl₂ obtained in step 4) at a        temperature of from about 500 to about 530° C. to obtain molten        CuCl salt and oxygen gas.

Alternatively, the Cu—Cl cycle may comprise a four step processcomprising the steps of

-   -   1) reacting Cu and dry HCl gas at a temperature of about 450° C.        to obtain hydrogen gas and molten CuCl salt;    -   2) subjecting solid CuCl and HCl to electrolysis at a        temperature of about 70 to about 90° C. to obtain Cu and an        aqueous slurry containing HCl and CuCl₂;    -   3) heating the aqueous slurry containing HCl and CuCl₂ at a        temperature of from about 375 to about 450° C. to obtain solid        CuOCuCl₂ and gaseous HCl; and    -   4) heating the solid CuOCuCl₂ at a temperature of from about 500        to about 530° C. to obtain molten CuCl salt and oxygen gas.

A further alternative allows the use of a Cu—Cl cycle that comprises athree step process comprising the steps of

-   -   1) reacting Cu and dry HCl gas at a temperature of about 450° C.        to obtain hydrogen gas and molten CuCl salt;    -   2) subjecting solid CuCl and HCl to electrolysis at a        temperature of about 70 to about 90° C. to obtain Cu and an        aqueous slurry containing HCl and CuCl₂;    -   3) heating the aqueous slurry containing HCl and CuCl₂ at a        temperature of from about 500 to about 530° C. to obtain molten        CuCl salt and oxygen gas.

A further alternative allows the use of a Cu—Cl cycle that comprisesanother three step process as follows:

-   -   1) subjecting CuCl and HCl aqueous solution at a temperature of        about 70 to 90° C. to obtain H2 and an aqueous slurry containing        HCl and CuCl₂;    -   2) heating the solid CuCl₂ and water to obtain solid CuOCuCl₂        and gaseous HCl;    -   3) heating the aqueous slurry containing HCl and CuCl₂ at a        temperature from about 500 to 530° C. to obtain molten CuCl salt        and oxygen gas.

DETAILED DESCRIPTION BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross section of a screw extruder heat exchangerfor high temperature steam generation;

FIG. 1 a illustrates the same cross section as shown in FIG. 1, butincludes a closed loop whereby a water-steam chamber can be flushed outand cleaned.

FIG. 2 illustrates the lower structure of the screw extruder steamgenerator shown in FIG. 1, and is a top plan and perspective view of asection along line 2-2 showing the arrangement of the screw dischargerfor the precipitates or slurry or both from the non-pure water, afterthe steam has been generated;

FIG. 3 illustrates a front cross-sectional view of a pull/push plate ina molten salt heat exchanger for high temperature steam generation;

FIG. 4 illustrates a front cross-sectional view of a two-stage heatexchanger steam generator for high temperature steam generation usingimpure water;

FIG. 5 illustrates a schematic representation of a two-stage steamgeneration loop;

FIG. 6 illustrates the energy requirement distribution of the Cu—ClCycle; and

FIG. 7 illustrates a simplified flow chart of a typical Cu—Clthermochemical cycle for the production of hydrogen gas from thedecomposition of water; and

FIG. 8 is a schematic representation of the benefits of using the heatexchanger-steam generator apparatus and process described herein inpetrochemical operations.

STRUCTURE, DESIGN AND OPERATION OF THE HEAT EXCHANGER-STEAM GENERATOR

One form of the apparatus of the present description is illustrated inFIGS. 1 and 2 of the accompanying drawings. A continuous production modescrew extruder-steam generator for steam generation of this invention isshown generally at 10 in FIG. 1, it consists of inner and outer annulartubes, 11 and 12, respectively. The inner tube 11 contains a rotaryscrew 14 to agitate and push molten salt to move downward through acentral or core chamber 13, surrounded by an outer chamber 25, bothbeing formed by the outer tube 12 and inner tube 11. The inner chamberhas an inlet where a feed 15 of molten CuCl at a temperature of fromabout 420 to about 900° C., usually about 530° C. is provided to theinner chamber 13. The base of the reactor has an outlet for removal ofsolidified CuCl shown at 24.

Non-pure water at a temperature ranging from about 0 to about 100° C.,and typically at 20° C. is fed at inlet 16 into the outer chamber orjacket 25. The chamber 25 also includes an inlet 19 at which acontinuous water stream at a temperature of about 0 to 100° C., andtypically from about 10 to about 40° C., with 20° C. being typical isfed to chamber 25. Water is sprayed onto the outside wall of the innertube 11 to form a water film. When the film is flowing downward, wateraccumulates, boils and vaporizes. The water can be introduced also by acontinuous flow stream via inlet 19. An outlet for the steam is providedat 20 from the outer chamber. The temperature of the steam generated isin the range of about 100 to about 500° C. and the optimum range isabout 300 to about 400° C. The temperature of the molten salt enteringthe inside tube is in the range of about 420 to about 900° C. and theoptimum range is about 450 to about 530° C. The steam pressure can be inthe range of about 0 to about 250 bar (gauge) and the optimum range isabout 0 to about 2 bar gauge so that high temperature steam can begenerated. The diameter of inner tube 11A is in the range of about 5 toabout 100 cm and the optimum range is about 15 to about 45 cm. The spacefor the flights of the screw, B is in the range of about 1 to about 10cm and the optimum range is about 2 to about 5 cm. The diameter of thescrew root, C, is in the range of about 1 to about 50 cm, and theoptimum range is about 5 to about 20 cm. It is noted that the outsidetube could be other than cylindrical in shape, for example, rectangularor square. Between the two inlets 16 and 19, and between the inlet 16and the outlet 20, within the chamber 25, the temperatures achievedprovide boiling water and high temperature steam, respectively.

The dimensions of the tubes 11 and 12, and the whole unit are selectedto ensure the most efficient heat transfer and the generation of hightemperature steam.

The molten salt can also be introduced from the top, by eithercontinuous melt stream or pouring in this form of the apparatus. Toavoid the attachment of the solidified salt onto the wall of the innerchamber 13 during the downward travel of the salt, a suitable lubricantsuch as grease (silicone) can be applied onto the wall.

In operation, the process in this apparatus can be conducted on acontinuous basis. The molten salt is introduced into the chamber 13 ofthe heat exchanger-steam generator and the water is introduced as aspray and as a continuous flow stream into the outer chamber 25. As themolten salt is pushed downwardly through the central chamber via theturning of screw 14, heat is transmitted to the water entering the outerchamber 25 and the height of the apparatus is selected to ensuresufficient heat transfer to generate high temperature steam from thewater. Boiling water Hb is produced in a lower portion of chamber 25which rises upwardly becoming high temperature steam Hs, which isremoved via outlet 20. As steam is formed from the non-pure water,impurities and salts are deposited in the bottom of the chamber 25.These may comprise a solid precipitate or slurry or both. Removal ofthese materials is managed in a suitable manner known to those skilledin the art and recovery of any valuable products can be undertaken usingknown methods. An extruder 23 can be placed in the outlet from chamber25 to assist in removal of the impurities/minerals etc. The molten CuClsolidifies as the heat is transferred from it to the water. As the saltcools it solidifies. Removal of the salt is undertaken in accordancewith known methods for removing such solids from industrial equipment.

In FIG. 3, there is illustrated an alternative structure for the heatexchanger-steam generator. The rotary screw of FIG. 1 is replaced with apush-pull plate arrangement shown generally at 40. A top plate 41 and abottom plate 42 are provided in an inner salt chamber 43. The plates 41and 42 may have the same diameter X, which allows the plates to engageinterior wall 45 of chamber 43. The molten salt can be fed through aside inlet 15 and a top inlet 46. Removal of solid salt 21 can beachieved by removing the bottom plate 42. Outer chamber 44 has the sameinlets and outlets found in the heat exchanger-steam generator shown inFIG. 1. However, in the arrangement shown here, the process is generallyconducted as a batch or semi-batch process.

FIG. 4 illustrates a further alternative arrangement for the heatexchanger-steam generator which employs a casting with a mould: moltensalt steam generator. The structure here is very similar to the annulartube arrangement shown in FIG. 3. The difference is that no device isused to assist passage of molten salt through the central chamber. Allother aspects of the apparatus are the same as found in the apparatus ofFIG. 3. To approach a continuous operation, a surface coating such as alubricant, for example grease is usually needed to assist the CuCl tomove downwardly. When the molten CuCl is poured into the heat exchanger,the lubricant, e.g. grease may be continuously applied, e.g. by sprayingonto the surface of the inside wall of the inner tube 11, as indicatedby element 15A in FIG. 4. Any other known methods for distributing alubricant such as grease onto the inside wall at appropriate locationsare suitable for this purpose.

FIG. 5 shows an alternative arrangement that comprises a two-stage steamgeneration loop. Instead of directly generating the steam by the heat ofmolten salt, secondary thermal fluids are utilized to extract the heatfrom the molten salt, and then the thermal fluid is allowed to transferits heat to the non-pure water to generate steam in a second stage heatexchanger. A big advantage of using secondary thermal fluid is that thenon-pure water can be introduced to the tube route rather than the shellpath so the precipitates from the water can be more easily removed.Another advantage is that any corrosion from the non-pure water on theoutside wall of the pipe that confines the molten salt is eliminated.Typical secondary fluids include thermal oil, high pressure gases suchas nitrogen, helium, argon, and air.

The illustrated apparatus of FIG. 5 comprises two heat exchangers 60 and70, each having a shell 65, 75 and tube 64, 74 design. The heatexchangers 60 and 70 are connected so that the secondary thermal fluidcirculates from shell 65 to shell 75 through conduits 50, 51 and 52. Inthe first stage heat exchanger 60, molten salt enters tube 64 which maybe provided with a rotating screw 61 for pushing the molten salt throughthe tube 64. Screw 61 can be replaced with an alternative device forpushing the molten salt or no device may be used. Solidified salt exitsat 24 and is removed in a suitable manner. Heat from the molten salt istransferred to the thermal oil in shell 65 which circulates throughconduit 5 to a second stage heat exchanger 70 into shell 75. Non-purewater is fed to the central tube 70 at inlet 16 and as it passes throughthe heat exchanger 70, it picks up heat from the circulating hightemperature thermal oil and turns to super heated steam, which isremoved from outlet 20. Precipitates or slurry or both collects in tube74 and can be removed by a suitable device, such as a rotating screw 71,and any valuable material can be recovered in conventional ways.

Description of How the Molten Salt is Handled in the Heat Exchanger

A portion of a pilot plant was constructed incorporating the molten saltheat exchanger described herein. Referring to FIG. 1, one can see howthe heat exchanger 10 handles molten salt 15 a, which involves the saltbeing mixed and the dimensions of the tube 13 in the hear exchanger 10being selected to ensure this mixing takes place.

A feed of molten salt 15 is introduced to the tube 13 and is then pusheddownwardly by the axial pushing force of the flights 13 b of the rotaryscrew 14. During the downward moving of the molten salt 15, the salt 15close to the inside wall of chamber 13 is cooled to a lower temperaturethan the molten salt 15 close to the screw flights 13 b and root 13 a.At the same time, heat carried by the molten salt 15 is transferredthrough the wall 11 of chamber 13 to the water or steam contained in theannulus (25). Due to the radial agitating force of the flights 13 b, thelower-temperature molten salt 15 close to the inside wall of chamber 13is agitated until it is farther from the wall and closer to the screwroot 13 a to mix with a portion of higher temperature molten salt 15. Atthe same time, other portions of higher temperature molten salt 15 areagitated until closer to the inside wall of chamber 13. Some portions ofmolten salt 15 may solidify when the salt is agitated closer to theinside wall of chamber 13 and is then agitated back to closer to theroot 13 a to solidify more salt or it is melted again. Through themixing generated by the screw flights 13 b, the heat in variouslocations of the molten salt stream is transferred to the wall ofchamber 13 and hence to the water in the chamber 25.

During the downward movement of the molten salt 15, the temperature ofthe salt becomes lower and lower. When the salt 15 moves near the bottomof chamber 13, all salt 15 has been solidified. At this time, the rotaryscrew 14 also serves as a granulator to avoid forming big chunks ofsolidified salt.

To achieve the functions as described above, e.g., the good mixing andgranulating, the dimensions of the screw 14 and chamber 13 and therotary speed are selected and controlled to be in an optimal range,which can be determined through routine experimentation. The channelwidth B is usually in the range of 1-50 cm and the optimal width is 2-20cm. The flight width (A-8) is in the range of 0.2-10 cm and the optimalrange is 1-4 cm. The helix angle Ha may be selected from those in therange of 5-85 degrees and the optimal range is 15-45 degrees. The rotaryspeed may be selected to be in the range of 0.5-5000 rpm and the optimalrange is 1-100 rpm. These parameters are based on the pilot design andin practice can be readily adjusted to ensure maximum heat transfer andsteam production.

Handling of Water Impurities in Non-Pure Water

Safe operation of the heat exchanger 10 is necessary to avoid crackingon the inside wall 17 of chamber 13. Cracking can be avoided byenhancing the thickness of the chamber wall 17 and by selecting suitablematerial for the inside wall of the tube 14, along with regular checksand maintenance.

When the water is evaporated on the outside wall of chamber 13,impurities will be concentrated in the remaining unevaporated waterwhich flows downward along the wall. During the downward movement on thewall, some impurities, such as salts, will precipitate. The precipitatesare entrained by the concentrated water to accumulate in the chamber 25.Due to the density difference of water and the precipitates, theprecipitates settle at the bottom of chamber 25. When the quantity ofprecipitates exceeds the height of screw discharger 23 after someruntime, the screw discharger will operate and remove the precipitatesto outside of chamber 25. The runtime depends on the steam generationrate and scale, and the screw discharger 23 can then accordingly operateintermittently or continuously.

To ensure the downward moving of the precipitated impurities withconcentrated water, preferably 1-10% of the water is not evaporated sothat the precipitated impurities can be entrained by the downwardflowing concentrated water on the outside wall of chamber 13. Multiplewater level gauges can be set to monitor the evaporation extent. Thewater level gauges could be any known gauges.

Referring now to FIG. 1 a, after some runtime, for example, 6 months,the outside wall of chamber 14 may be covered by a layer of precipitatedimpurities to foul the chamber and affect the efficient operation of theheat exchanger 10. To remove the precipitates on the wall, the processis slowed or stopped, and simultaneously the water flow rate isincreased at inlet 16 to a higher value than normal, and the chamber 13is filled with water to reach the water level of inlet 16, and then thewater is pumped out through inlet 19 (now serving as an outlet) by pump100 back to inlet 16 to form a closed liquid water loop to dissolve theprecipitates and clean the outside wall of chamber 15. The speed of thewater flow is selected to be in the range of 5-30 m/s. After cleaning,the closed water loop formed by inlets 16 and 19 is disconnected, thenthe water flow rate of inlet 16, is restarted or the molten saltprocessing is restarted or the molten salt processing is speeded up. Theconnection or disconnection of inlets 16 and 19 is controlled by valve99. Some cleaning acids, such as, for example dilute HCl or HNO₃, canalso be used as additives or agents, for the removal of water-insolubleimpurities precipitated on the wall.

The precipitates removed from chamber 25 may carry water or be anaqueous slurry. The slurry can be conveyed to a filtration system toextract water and the extracted water can be reused for steamgeneration. The filtration can be conducted using any known system.

The impurities do not have to be precipitated, as they can also beproduced in a highly concentrated aqueous solution which accumulates atthe bottom of chamber 25. The screw discharger 23 can remove the highlyconcentrated water, or the screw discharger can be replaced by a simplepipe wherein the concentrated water can be pumped out. In this case anextra loop may be required to recover the water from the highlyconcentrated aqueous solution or disposal of it may be needed.

The equipment and technology described herein are compatible with mosttypes of non-pure water and especially suitable for geographical areaswhere fresh and high quality water are not as plentiful as other areas,or where saline and brackish water are richer than fresh, high qualitywater, e.g., industrial regions for oil sands extraction and upgradingwhere the use of fresh and high quality water is strictly limited anddistributed.

Brackish water is water that has more salinity than fresh water, but notas much as seawater. It may result from mixing of seawater with freshwater, as in estuaries, or it may occur in brackish fossil aquifers.Certain human activities can produce brackish water, in particularcertain civil engineering projects such as dikes and the flooding ofcoastal marshland to produce brackish water pools for freshwater prawnfarming. Brackish water is also the primary waste product of thesalinity gradient power process. Because brackish water is hostile tothe growth of most terrestrial plant species, without appropriatemanagement it is damaging to the environment. Technically, brackishwater contains between 0.5 and 30 grams of salt per litre—more oftenexpressed as 0.5 to 30 parts per thousand (ppt or %_(o)).

Pure water is a non-conductive substance that is toxic to life, andcorrosive of most metals. Impure water is water that has impurities,such as salts, hardness, metal ions, and so on.

There are benefits to using the present technology in conjunction withpetrochemical processes and these are illustrated in FIG. 8. Non-purewater, e.g. brackish water, can be used to produce hydrogen that can beused for operations, such as oil sands upgrading, refineries, enrichmentof concentration of hydrogen in syngas, among others. Also, oxygen canbe used for gasification of upgrading residuals or coal, improvingcombustion, reducing the use of air heating, and lowering NOx emissions.This technology is capable of using non-pure water to produce hydrogenand oxygen for upstream and downstream units of petrochemical plantoperations.

FIG. 6 illustrates schematically the energy inputs and outputs for atypical CuCl Cycle derived from incorporating the present technology andequipment, which are considered to be significant.

FIG. 7 is a simplified representation of a prior art Cu—Cl Cycle, whichis described in more detail in the previously referenced US PatentPublication No. 2010/012987. Reference may be had to the specific partsof this patent application which describe the contents of FIG. 7 indetail, where it appears as FIG. 5. In FIG. 7, an input of water isincluded. This represents an example of how the present technology couldbe combined with the Cu—Cl cycle.

The materials used to construct the apparatus of the present technologymay be selected in accordance with the operating parameters of theequipment. The selection is within the common knowledge of a personskilled in the art.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.Modifications which fall within the scope of the present invention willbe apparent to those skilled in the art, in light of a review of thisdisclosure, and such modifications are intended to fall within theappended claims.

1. In a high temperature industrial process where heat recovery isdesired, the improvement comprising transferring heat from a hightemperature molten or gaseous material obtained in the high temperatureindustrial process, to generate high temperature steam from non-purewater, with the impurities in the water being reduced to a precipitate,a slurry or a concentrated aqueous solution, which can be disposed of,or subjected to further processing.
 2. The process as claimed in claim1, comprising generating high temperature steam in a heat exchangeprocess, wherein heat from molten material is supplied to non-pure waterto produce high temperature steam, with the impurities in the waterbeing reduced to a precipitate, a slurry or a concentrated aqueoussolution, which can be disposed of, or subjected to further processing.3. The process as claimed in claim 1, comprising generating hightemperature steam in a heat exchange process, wherein the steam isgenerated from a two-stage steam generation loop which comprises twoheat exchanges, a first-stage heat exchange comprising transferring heatfrom molten material to a thermal fluid circulating to a second-stageheat exchange, and back again to the first-stage heat exchange; heatfrom the thermal fluid being transferred to non-pure water in thesecond-stage heat exchange to produce high temperature steam from whichhydrogen gas is produced, and impurities in the water are reduced to aprecipitate, a slurry or a concentrated aqueous solution, which can bedisposed of, or subjected to further processing.
 4. The process asclaimed in claim 1, wherein the industrial process is a thermochemicalCu—Cl cycle for producing hydrogen gas from water decomposition whichcomprises supplying heat to the non-pure water from molten CuCl toproduce high temperature steam for the production of hydrogen gas, withthe impurities in the water being reduced to a precipitate, a slurry ora concentrated aqueous solution, which can be disposed of, or subjectedto further processing.
 5. The process as claimed in claim 1, wherein theindustrial process is a thermochemical Cu—Cl cycle for producinghydrogen gas from water decomposition which comprises the generation ofsteam from non-pure water using a two-stage steam generation loop whichcomprises two heat exchanges, a first-stage heat exchange comprisingtransferring heat from molten CuCl to a thermal fluid circulating to asecond-stage heat exchange, and back again to the first-stage heatexchange; heat from the thermal fluid being transferred to non-purewater in the second-stage heat exchange to produce high temperaturesteam from which hydrogen gas is produced, and impurities in the waterare reduced to a precipitate, a slurry or a concentrated aqueoussolution, which can be disposed of, or subjected to further processing.6. A device for use in a high temperature industrial process where heatrecovery is required and high temperature steam is produced whichcomprises using a tube and shell heat exchanger, the tube is arranged toreceive a high temperature molten or gaseous material obtained from thehigh temperature industrial process and the shell is arranged to receivenon-pure water to which heat is transferred from the high temperaturemolten or gaseous material in the tube, which then generates hightemperature steam from the non-pure water, with the impurities in thenon-pure water being reduced to a precipitate, a slurry or aconcentrated aqueous solution, which can be disposed of, or subjected tofurther processing.
 7. A device for use in a high temperature industrialprocess where heat recovery is desired and high temperature steam isproduced, comprising a two-stage steam generation loop which comprisestwo heat exchangers, each having a central tube and surrounding shell,the first-stage heat exchanger arranged for high temperature molten orgaseous material to pass through its central tube and the surroundingshell is arranged to receive a secondary thermal fluid to circulate inthe surrounding shell to absorb heat from the high temperature molten orgaseous material, the surrounding shell being in fluid communicationwith the shell in the second-stage heat exchanger to permit circulationof the heated thermal fluid from one shell to the other and back againto the shell in the first-stage heat exchanger; the central tube of thesecond stage heat exchanger arranged to receive non-pure water whichabsorbs heat from the thermal fluid to generate high temperature steamfor use in the high temperature industrial process, and impurities inthe water are reduced to a precipitate, a slurry or a concentratedaqueous solution, which can be disposed of, or subjected to furtherprocessing.
 8. The device as claimed in claim 6, wherein the industrialprocess is a thermochemical Cu—Cl cycle for the production of hydrogenfrom water decomposition and the molten material is CuCl salt, and thehigh temperature steam is used to produce the hydrogen gas fromdecomposition of water in the thermochemical Cu—Cl cycle.
 9. The deviceas claimed in claim 8, wherein the molten CuCl is received in the tubeof the heat exchanger and passes therethrough with the assistance of atleast one of gravity, a push-pull plate or a helical screw.
 10. Thedevice as claimed in claim 8, wherein the molten CuCl passes through thetube of the heat exchanger at a rate that allows the production of hightemperature steam at a temperature suitable for the production ofhydrogen gas from the decomposition of water in the thermochemical Cu—Clcycle.
 11. The device as claimed in claim 8, wherein the tube wall istreated with lubricant to assist passage of molten CuCl through the tubeof the heat exchanger, in at least one of the following ways: in advanceof the device being used, on a periodic basis and on a continuous basisduring use of the device.
 12. The device as claimed in claim 8, whereinthe shell walls are washed with water or water containing cleaners orboth to remove any adhered impurities that foul the reactor, the washingtaking place either when the device is in use or when the device is notin use.
 13. The device as claimed in claim 9, wherein a helical screw isused and assists the passage of molten CuCl through the tube as itpasses from a molten state to a solid state, as well as the efficientheat transfer from the molten CuCl to the non-pure water.